Control Structure - Allen-Bradley Logix5000 Reference Manual

Mnemonic Data Type
.EN BOOL
.DN BOOL
.EM BOOL
.LEN DINT
.POS DINT
Description:
Arithmetic Status Flags:
Fault Conditions:

CONTROL Structure

Description:
The enable bit indicates that the LFL instruction is enabled.
The done bit is set to indicate that the LIFO is full (.POS = .LEN). The .DN bit inhibits loading
the LIFO until .POS < .LEN.
The empty bit indicates that the LIFO is empty. If .LEN ≤ 0 or .POS < 0, both the .EM bit and
.DN bit are set.
The length specifies the maximum number of elements the LIFO can hold at one time.
The position identifies the location in the LIFO where the instruction will load the next value.
Use the LFL instruction with the LFU instruction to store and retrieve data in a
last-in/first-out order. When used in pairs, the LFL and LFU instructions
establish an asynchronous shift register.
Typically, the Source and the LIFO are the same data type.
When enabled, the LFL instruction loads the Source value into the position in
the LIFO identified by the .POS value. The instruction loads one value each time
the instruction is enabled, until the LIFO is full.
IMPORTANT
Not affected
A major fault will occur if
(starting element + .POS) > LIFO array size
Rockwell Automation Publication 1756-RM003N-EN-P - October 2011
Array (File)/Shift Instructions (BSL, BSR, FFL, FFU, LFL, LFU)
You must test and confirm that the instruction doesn't
change data that you don't want it to change.
The LFL instruction operates on contiguous memory. In
some cases, the instruction loads data past the array into
other members of the tag. This happens if the length is too
big and the tag is a user-defined data type.
Fault type
4
Chapter 9
Fault code
20
423